Electronic device manufacturers are constantly striving to produce a rich interface for users. Conventional devices utilize visual and auditory cues to provide feedback to a user. In some interface devices, kinesthetic feedback (such as, without limitation, active and passive force feedback), and/or tactile feedback (such as, without limitation, vibration, texture, and heat), is also provided to the user, more generally known collectively as “haptic feedback.” Haptic feedback provides additional cues that enhance and simplify the user interface.
A device may incorporate a variety of technologies for providing haptic feedback, including both active and passive devices. Active haptic feedback devices, including, for example, motors, add energy to a system; passive devices, such as brakes, remove energy from the system.
Conventional passive haptic actuators utilize magnetic particle brakes, magnetorheologic or electrorheologic brakes, or magnetic (non-friction) brakes. Each of these conventional approaches suffers from disadvantages. These conventional devices are expensive and difficult to produce. They are also larger than is practical for implementation in small, handheld devices, such as cell phones, personal digital assistants, and the like.
Conventional magnetic particle brakes utilize a powder comprising particles of a magnetic material. When a current is applied, the particles line up and cause the powder to expand. Rheologic fluid brakes utilize a fluid that changes viscosity when a current is applied. These types of devices are expensive because of the cost of the materials and because of the need to retain the fluid within the device.
A magnetic brake generates a magnetic field, and when a piece of metal passes through the magnetic field, an anti-current is generated, causing a resistance to movement of the metal. Conventional magnetic brakes require the metal to be moving at high speed to be effective. Thus, these devices are not practical for relatively slow moving user interface elements.